Process For Preparing Semipermeable Membranes - Patent 7708150

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United States Patent: 7708150


































 
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	United States Patent 
	7,708,150



 Kurth
 

 
May 4, 2010




Process for preparing semipermeable membranes



Abstract

The invention provides methods for preparing reverse osmosis membranes
     having improved permeability as well as membranes prepared by such
     methods.


 
Inventors: 
 Kurth; Christopher J. (Chaska, MN) 
 Assignee:


GE Osmonics, Inc.
 (Minnetonka, 
MN)





Appl. No.:
                    
11/220,005
  
Filed:
                      
  September 6, 2005

 Related U.S. Patent Documents   
 

Application NumberFiling DatePatent NumberIssue Date
 PCT/US2004/006484Mar., 2004
 60451761Mar., 2003
 

 



  
Current U.S. Class:
  210/500.38  ; 210/490; 210/500.27; 264/48; 264/49
  
Current International Class: 
  B01D 39/14&nbsp(20060101); B01D 39/00&nbsp(20060101); B01D 67/00&nbsp(20060101); B29C 44/04&nbsp(20060101); B29C 67/20&nbsp(20060101)
  
Field of Search: 
  
  










 210/500.38,490,500.27,653,654,500.37,500.39,500.41 427/244-245 264/41,48-49
  

References Cited  [Referenced By]
U.S. Patent Documents
 
 
 
3744642
July 1973
Scala et al.

4277344
July 1981
Cadotte

4619767
October 1986
Kamiyama et al.

4765897
August 1988
Cadotte et al.

4812270
March 1989
Cadotte et al.

4830885
May 1989
Tran et al.

4948506
August 1990
Lonsdale et al.

4948507
August 1990
Tomaschke

4983291
January 1991
Chau et al.

5021160
June 1991
Wolpert

5128041
July 1992
Degen et al.

5147553
September 1992
Waite

5152901
October 1992
Hodgdon

5178766
January 1993
Ikeda et al.

5614099
March 1997
Hirose et al.

5658460
August 1997
Cadotte et al.

5843351
December 1998
Hirose et al.

5922203
July 1999
Tomaschke

6026968
February 2000
Hachisuka et al.

6368507
April 2002
Koo et al.

6521130
February 2003
Kono et al.

6783937
August 2004
Hou et al.

6851561
February 2005
Wu et al.

6860393
March 2005
Hou et al.

6878278
April 2005
Mickols

6913694
July 2005
Koo et al.

7081202
July 2006
Ohara et al.



 Foreign Patent Documents
 
 
 
0474370
Oct., 1996
EP

02002827
Jan., 1990
JP

WO2004/078328
Sep., 2006
WO



   
 Other References 

International Search Report for PCT/US2004/006484. cited by other.  
  Primary Examiner: Fortuna; Ana M


  Attorney, Agent or Firm: Viksnins Harris & Padys PLLP



Parent Case Text



CROSS-REFERENCE TO RELATED APPLICATIONS


This application is a continuation under 35 USC 111(a) of
     PCT/US2004/006484 filed Mar. 3, 2004 and published in English on Sep. 16,
     2004 as WO 2004/078328 A1, which claimed priority from U.S. Provisional
     Application No. 60/451,761, filed Mar. 3, 2003, which applications and
     publications are incorporated herein by reference.

Claims  

I claim:

 1.  A method for preparing a reverse osmosis membrane having improved flux properties comprising treating a starting reverse osmosis membrane with an ammonium salt comprising: (1) a
cation selected from trimethylbenzylammonium, dibutylammonium, tripropylammonium, hexylammonium, ethylammonium, triethanolammonium, trimethylammonium, dimethylammonium, dipropylammonium, diisopropylethylammonium, triethylammonium, tetraethylammonium, or
diethylammonium;  and (2) a suitable anion other than nitrate, borate, or perchlorate;  and optionally drying to provide the reverse osmosis membrane having improved flux properties.


 2.  The method of claim 1 wherein the cation is hexylammonium, ethylammonium, triethanolammonium, trimethylammonium, dimethylammonium, dipropylammonium, diisopropylethylammonium, triethylammonium, tetraethylammonium, or diethylammonium.


 3.  The method of claim 1 wherein the cation is tetraethylammonium.


 4.  The method of claim 1 wherein the anion is floride, chloride, bromide, iodide, acetate, trichloroacetate, sulfate, methanesulfonate, phosphate, toluenesulfonate, or the anion of acetoacetamide.


 5.  The method of claim 1 further comprising preparing the starting reverse osmosis membrane by coating a porous support backing material with an aqueous solution of a polyamine, optionally removing excess solution, and contacting the coated
porous support backing material with an organic solution of a polyacyl halide, polysulfonyl halide or polyisocyanate to provide the starting reverse osmosis membrane as a condensation reaction product.


 6.  The method of claim 5 wherein the polyamine is an aromatic di or tri amine or a mixture thereof.


 7.  The method of claim 5 wherein the polyacylhalide is an aromatic di or tri acid halide.


 8.  The method of claim 1 wherein the starting reverse osmosis membrane has been dried prior to the treating.


 9.  The method of any one of claims 1 wherein the treating is carried out at a pH of greater than 8.


 10.  The method of any one of claims 1 wherein the treating is carried out at a pH of greater than 10.


 11.  A reverse osmosis membrane that has a salt in the pores of the membrane, wherein the salt comprises (1) a cation selected from trimethylbenzylammonium, dibutylammonium, tripropylammonium, hexylammonium, ethylammonium, triethanolammonium,
trimethylammonium, dimethylammonium, dipropylammonium, diisopropylethylammonium, triethylammonium, tetraethylammonium, or diethylammonium;  and (2) an anion other than nitrate, borate, or perchlorate.


 12.  The membrane of claim 11 which has a porous support backing material, having pores and a salt in the pores wherein the salt comprises (1) a cation selected from trimethylbenzylammonium, dibutylammonium, tripropylammonium, hexylammonium,
ethylammonium, triethanolammonium, trimethylammonium, dimethylammonium, dipropylammonium, diisopropylethylammonium, triethylammonium, tetraethylammonium, or diethylammonium;  and (2) an anion other than nitrate, borate, or perchlorate.


 13.  The membrane of claim 11 wherein the anionin is a halide, (C.sub.1-C.sub.6)alkanoate halo(C.sub.1-C6)alkanoate, sulfate, (C.sub.1-C.sub.6)alkylsulfonate, phosphate, toluenesulfonate, or the anion of acetoacetamide.


 14.  A method for preparing a reverse osmosis membrane having improved flux properties comprising treating a starting reverse osmosis membrane with an ammonium salt comprising: (1) a cation selected from trimethylbenzylammonium, dibutylammonium,
tripropylammonium, hexylammonium, ethylammonium, triethanolammonium, trimethylammonium, dimethylammonium, dipropylammonium, diisopropylethylammonium, triethylammonium, or diethylammonium and (2) subjecting the reverse osmosis membrane to a post
treatment.


 15.  The method of claim 14 wherein the cation is hexylammonium, ethylammonium, triethanolammonium, trimethylammonium, dimethylammonium, dipropylammonium, diisopropylethylammonium, triethylammonium, or diethylammonium.


 16.  The method of claim 14 wherein the post treatment comprises contacting the reverse osmosis membrane with hypochlorite ions.


 17.  The method of claim 14 wherein the starting reverse osmosis membrane has been dried prior to the treating.


 18.  The method of any one of claims 14 wherein the treating is carried out at a pH of greater than 8.  Description  

BACKGROUND OF THE INVENTION


Various techniques are used for effecting separation using asymmetric or composite membranes including selective permeation, ultrafiltration and reverse osmosis.  One example of reverse osmosis separation is a desalination process in which
seawater, contaminated water, or brackish water is rendered potable.  Desalination of such water is often necessary to provide large amounts of relatively nonsalty water for industrial, agricultural, or home use.  Such desalination can be effected by
forcing water through a reverse osmosis membrane which retains the contaminants or salts.  Typical reverse osmosis membranes have a very high salt rejection coefficient and possess the ability to pass a relatively large amount of water through the
membrane at relatively low pressures.


Various U.S.  patents describe reverse osmosis membranes and supports that are useful in industrial processes.  See for example: U.S.  Pat.  Nos.  4,830,885, 3,744,642, 4,277,344, 4,619,767, 4,830,885, and 4,830,885.


U.S.  Pat.  Nos.  4,765,897 and 4,812,270 discusses polyamide membranes that are reported to be useful for water softening applications.  The membranes are prepared by treating a polyamide reverse osmosis membrane with a strong mineral acid
followed by treatment with a rejection enhancing agent.


Subsequently, U.S.  Pat.  No. 4,983,291 reported semipermeable membranes that are subjected to treatment with acids or certain acid derivatives and dried to provide a membrane that maintains high flux with a concurrent rejection rate.


Despite the above disclosures, there remains a need for reverse osmosis membranes having useful flux and retention properties.  In particular, there is a need for reverse osmosis membranes that possess improved flux characteristics while
maintaining useful rejection characteristics.


SUMMARY OF THE INVENTION


Applicant has discovered a method for preparing semipermeable reverse osmosis membranes having improved flux properties.


Accordingly, the invention provides a method for preparing a reverse osmosis membrane having improved flux properties comprising treating a starting reverse osmosis membrane with an ammonium salt comprising: 1) a cation selected from
trimethylbenzylammonium, dibutylammonium, tripropylammonium, hexylammonium, ethylammonium, triethanolammonium, trimethylammonium, dimethylammonium, dipropylammonium, diisopropylethylammonium, triethylammonium, tetraethylammonium, or diethylammonium; and
2) a suitable anion other than nitrate, borate, or perchlorate; and optionally drying to provide the reverse osmosis membrane having improved flux properties.


The invention also provides a method of improving the permeability of a reverse osmosis membrane comprising, treating a reverse osmosis membrane with an aqueous solution of an ammonium salt comprising: 1) a cation selected from
trimethylbenzylammonium, dibutylammonium, tripropylammonium, hexylammonium, ethylammonium, triethanolammonium, trimethylammonium, dimethylammonium, dipropylammonium, diisopropylethylammonium, triethylammonium, tetraethylammonium, or diethylammonium; and
2) a suitable anion other than nitrate, borate, or perchlorate; drying; and optionally recovering the membrane.


The invention also provides a reverse osmosis membrane prepared by a method of the invention.


U.S.  Pat.  No. 4,983,291 reported that the flux of a membrane could be maintained following drying by treatment with an acid selected from the group consisting of hydroxypolycarboxylic acids, polyaminoalkylene polycarboxylic acids, sulfonic
acids, amino acids, amino acid salts, amine salts of acids, polymeric acids and inorganic acids prior to drying.  Applicant has discovered that treatment of reverse osmosis membranes with a specific set of ammonium salts provides membranes with
significantly improved flux.  Additionally, the treatments of the invention do not significantly detract from the salt rejecting properties of the membrane.


The invention also provides a method for preparing a reverse osmosis membrane having improved flux properties comprising treating a starting reverse osmosis membrane with an ammonium salt comprising: (1) a cation selected from
trimethylbenzylammonium, dibutylammonium, tripropylammonium, hexylammonium, ethylammonium, triethanolammonium, trimethylammonium, dimethylammonium, dipropylammonium, diisopropylethylammonium, triethylammonium, tetraethylammonium, or diethylammonium and
(2) subjecting the reverse osmosis membrane to post treatment. 

DETAILED DESCRIPTION OF THE INVENTION


Reverse Osmosis Membranes


Reverse osmosis membranes which can be treated according to the methods of the invention include the reaction product of polyacyl halides, polysulfonyl halides or polyisocyanates and polyamines or bisphenols.  The reaction product is typically
deposited within and/or on a porous support backing material.


Reverse osmosis membranes can be prepared using methods that are generally known in the art, for example using methods similar to those described in U.S.  Pat.  Nos.  3,744,642; 4,277,344; 4948507; and 4,983,291.  Such methods entail coating an
aqueous solution of a polyamine or a bisphenol, and preferably a polyamine, on a porous support backing material.  Thereafter, the surface of the coated support material is optionally freed of excess amine solution and is contacted with an organic
solution of a polyacyl halide, polysulfonyl halide or polyisocyanate to provide the reverse osmosis membrane, which can be utilized as a starting material in the method of the invention.  These membranes may further be dried from glycerin, or drying
agents disclosed in aforementioned patents.


The porous support backing material typically comprises a polymeric material containing pore sizes which are of sufficient size to permit the passage of permeate therethrough, but are not large enough so as to interfere with the bridging over of
the resulting ultrathin reverse osmosis membrane.  Examples of porous support backing materials which may be used to prepare the desired membrane composite of the present invention will include such polymers as polysulfone, polycarbonate, microporous
polypropylene, the various polyamides, polyimines, polyphenylene ether, various halogenated polymers such as polyvinylidine fluoride, etc.


The porous support backing material may be coated utilizing either a hand coating or continuous operation with an aqueous solution of monomeric polyamines or to render the resulting membrane more resistant to environmental attacks of monomeric
secondary polyamines.  These monomeric polyamines may comprise cyclic polyamines such as piperazine, etc.; substituted cyclic polyamines such as methyl piperazine, dimethyl piperazine, etc.; aromatic polyamines such as m-phenylenediamine,
o-phenylenediamine, p-phenylenediamine, etc.; substituted aromatic polyamines such as chlorophenylenediamine, N,N'-dimethyl-1,3-phenylenediamine, etc.; multi-aromatic ring polyamines such as benzidine, etc.; substituted multi-aromatic ring polyamines
such as 3,3'-dimethylbenzidene, 3,3'-dichlorobenzidine, etc.; or a mixture thereof depending on the separation requirements as well as the environmental stability requirements of the resulting membranes.


The solution which is utilized as the carrier for the aromatic polyamine will typically comprise water in which the aromatic polyamine will be present in an amount in the range of from about 0.1 to about 20% by weight of the solution and which
will have a pH in the range of from about 7 to about 14.  The pH may either be the natural pH of the amine solution, or may be one afforded by the presence of a base.  Some examples of these acceptors will include sodium hydroxide, potassium hydroxide,
sodium carbonate, triethylamine, N,N'-dimethylpiperazine, etc. Other additives in the amine solution may include surfactants, amine salts (for example see U.S.  Pat.  No. 4,984,507), and/or solvents (for example see U.S.  Pat.  No. 5,733,602).


After coating the porous support backing material with the aqueous solution of the aromatic polyamine, the excess solution is optionally removed by suitable techniques.  Following this, the coated support material is then contacted with an
organic solvent solution of the aromatic polyacyl halide.  Examples of aromatic polyacyl halides which may be employed will include di- or tricarboxylic acid halides such as trimesoyl chloride (1,3,5-benzene tricarboxylic acid chloride), isophthaloyl
chloride, terephthaloyl chloride, trimesoyl bromide (1,3,5-benzene tricarboxylic acid bromide), isophthaloyl bromide, terephthaloyl bromide, trimesoyl iodide (1,3,5-benzene tricarboxylic acid iodide), isophthaloyl iodide, terephthaloyl iodide, as well as
mixtures of di-tri, tri-tri carboxylic acid halides, that is, trimesoyl halide and the isomeric phthaloyl halides.  Alternative reactants to the aromatic polyacyl halide include aromatic di or tri sulfonyl halides, aormatic di or tri isocyanates,
aromatic di or tri chloroformates, or aromatic rings substituted with mixtures of the above substituents.  The polyacyl halides may be substituted to render them more resistant to further environmental attack.


The organic solvents which are employed in the process of this invention will comprise those which are immiscible with water, immiscible or sparingly miscible with polyhydric compounds and may comprise paraffins such as n-pentane, n-hexane,
n-heptane, cyclopentane, cyclohexane, methylcyclopentane, naphtha, Isopars, etc. or halogenated hydrocarbon such as the Freon series or class of halogenated solvents.


Treatment According to the Invention


According to the invention, a reverse osmosis membrane, for example a membrane prepared as described above, is exposed to a salt A.sup.+X.sup.- or a mixture thereof for a period of time ranging from about 1 second to about 24 hours.  The exposure
of the membrane is usually affected at temperatures ranging from ambient up to about 90.degree.  C. or more and preferably at a temperature in the range of from about 20.degree.  to about 40.degree.  C.


Following exposure of the membrane, it is dried at elevated temperature (for example, up to about 170.degree.  C.) for a period of time ranging from about 30 seconds to about 2 hours or more in duration.


Membranes prepared according to the methods of the invention typically have certain specific ammonium salts in or on the membrane.  Accordingly, the invention provides a reverse osmosis membrane having improved permeability that has an ammonium
salt in or on the membrane and optionally in the pores of the porous support backing material.


The term "A value" in the context of the present invention represents the water permeability of a membrane and is represented by the cubic centimeters of permeate water over the square centimeters of membrane area times the seconds at the
pressure measured in atmospheres.  An A value of 1 is essentially 10.sup.-5 cm.sup.3 of permeate over the multiplicand of 1 centimeter squared of membrane area times 1 second of performance at a net driving pressure of one atmosphere.  In the context of
the present invention, A values given herein have the following unit designation: 10.sup.-5 cm.sup.3/(cm.sup.2secatm.) or 10.sup.-5 cm/(secatm) at 25.degree.  C.


Membranes prepared according to the methods of the invention can also be subjected to post treatment for example, to improve performance, increase stability, change fouling characteristics, modify physical properties, modify flux, or modify
retention properties.  Suitable post treatment methods are known in the art, see for example, Cadotte (U.S.  Pat.  No. 4,277,344), Jons et al. (U.S.  Pat.  No. 5,876,602) and Hirose et al. (U.S.  Pat.  No. 6,171,497).  According to one embodiment of the
invention, the reverse osmosis membrane can be post treated with an oxidizing agent.  In another embodiment, the reverse osmosis membrane can be post treated with a chlorine source (e.g., hypochlorite).


The following examples are given for illustration and are not limiting.


EXAMPLE 1


A 0.425M solution of each tetraethylammonium salt with 1% triethylamine was applied to the face of an Osmonics AK RO membrane for 30 seconds.  The solution was drained and the membrane dried at 120.degree.  C. for 8 minutes.  A control was
prepared as described above, without the tetraethylammonium salt.  Testing was conducted at 105 psi at a concentration of 500 ppm sodium chloride.  A values are reported in units of 10.sup.-5 cm/(secatm) at 25.degree.  C. Results for several salts are
provided in Table 1.


 TABLE-US-00001 TABLE 1 Anion A Value Passage Control 22.5 4 Chloride 43.1 10 Bromide 35.5 9.2 Iodide 12.1 12.2 Acetate 44 15.9 Trichloroacetate 32.4 11.2 Sulfate 31.3 4.8 Methanesulfonate 39.7 13 Phosphate 27.3 7.4 Toluenesulfonate 28.8 5.1
Acetoacetamide Anion 38 12.1


EXAMPLE 2


A membrane prepared as in Example 1 was rolled into a spiral wound element.  The element was flushed with water to remove residual chemicals, and then run on a solution containing 100 ppm NaOCl for a period of 20 minutes.  Subsequent testing at
65 psig on 500 ppm NaCl gave the membrane an A value of 45 and a salt passage of 3%.


All publications, patents, and patent documents are incorporated by reference herein, as though individually incorporated by reference.  The invention has been described with reference to various specific and preferred embodiments and techniques. However, it should be understood that many variations and modifications may be made while remaining within the spirit and scope of the invention.


* * * * *























				
DOCUMENT INFO
Description: Various techniques are used for effecting separation using asymmetric or composite membranes including selective permeation, ultrafiltration and reverse osmosis. One example of reverse osmosis separation is a desalination process in whichseawater, contaminated water, or brackish water is rendered potable. Desalination of such water is often necessary to provide large amounts of relatively nonsalty water for industrial, agricultural, or home use. Such desalination can be effected byforcing water through a reverse osmosis membrane which retains the contaminants or salts. Typical reverse osmosis membranes have a very high salt rejection coefficient and possess the ability to pass a relatively large amount of water through themembrane at relatively low pressures.Various U.S. patents describe reverse osmosis membranes and supports that are useful in industrial processes. See for example: U.S. Pat. Nos. 4,830,885, 3,744,642, 4,277,344, 4,619,767, 4,830,885, and 4,830,885.U.S. Pat. Nos. 4,765,897 and 4,812,270 discusses polyamide membranes that are reported to be useful for water softening applications. The membranes are prepared by treating a polyamide reverse osmosis membrane with a strong mineral acidfollowed by treatment with a rejection enhancing agent.Subsequently, U.S. Pat. No. 4,983,291 reported semipermeable membranes that are subjected to treatment with acids or certain acid derivatives and dried to provide a membrane that maintains high flux with a concurrent rejection rate.Despite the above disclosures, there remains a need for reverse osmosis membranes having useful flux and retention properties. In particular, there is a need for reverse osmosis membranes that possess improved flux characteristics whilemaintaining useful rejection characteristics.SUMMARY OF THE INVENTIONApplicant has discovered a method for preparing semipermeable reverse osmosis membranes having improved flux properties.Accordingly, the invention provides a method for prepari